The mating behavior of Saccharomyces cerevisiae represents one of the simplest systems of fundamental interest in the study of cell-cell interaction. The signal for mating (or fusion) of cells of opposite mating types a and alpha is mediated by the mating type specific polypeptide pheromones, the a and alpha factors. The alpha factor is a peptide pheromone of 13 amino acids made by the alpha cells. A precursor peptide of at least 24 amino acids is first made before it is processed and transported outside of the cells. We propose to clone the alpha factor structural gene of yeast. This is possible because the amino acid sequence of the alpha factor is known thus allowing us to synthesize specific oligonucleotide probes which can be used for screening the alpha factor structural gene sequence. We intend to end label these probes and then use them as primers for the synthesis of alpha specific cDNA. The cDNA will be used as probes for the screening of the alpha factor structural gene clone.